In general, a touch screen panel which is attached onto display devices including a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting diode (OLED), an active matrix organic light emitting diode (AMOLED), and the like is one of input devices which generate a signal corresponding to a relevant location when an object such as a finger or pen is touched. The touch screen panel is used in very wide fields including a small portable terminal, an industrial terminal, a digital information device (DID), and the like. Various types of touch screen panels in the related art are disclosed, but a resistive touch screen panel in which a manufacturing process is simple and manufacturing cost is small is most widely used. However, the resistive touch screen panel has problems in that it is inconvenient to use the resistive touch screen panel, multi-touch and gesture recognition are difficult, and a detection error occurs because transmittance is low and pressure needs to be applied.
Contrary to this, since the capacitive touch screen panel has advantages in that the transmittance is high, soft touch may be recognized, and the multi-touch and the gesture recognition are excellent, the capacitive touch screen panel is increasingly penetrating a market.
FIG. 1 illustrates one example of a capacitive touch screen panel in the related art. Referring to FIG. 1, transparent conductive films are formed on upper and lower surfaces of a transparent substrate 2 made of plastic or glass and voltages applying metallic electrodes 4 are formed at four respective corners of the transparent substrate 2. The transparent conductive film is made of transparent metal such as indium tin oxide (ITO) or antimony tin oxide (ATO). In addition, the metallic electrodes 4 formed at four corners of the transparent conductive film are formed by being printed with conductive metal having low resistivity, such as silver (Ag). A resistance network is formed on the periphery of the metallic electrodes 4. The resistance network is formed with a linearization pattern in order to uniformly transmit a control signal to the entire surface of the transparent conductive film. In addition, a passivation film is coated on the top of the transparent conductive film including the metallic electrode 4.
In the capacitive touch screen panel, when high-frequency alternating voltage is applied to the metallic electrode 4, the high-frequency alternating voltage spreads over a front surface of the transparent substrate 2. In this case, when the transparent conductive film on the top of the transparent substrate 2 is lightly touched with a finger 8 or a conductive touch input means, a current sensor embedded in a controller 6 senses a change in current while a predetermined amount of current is absorbed in a body and a current amount is calculated in each of four metallic electrodes 4 to recognize a touch point.
However, since a capacitive touch screen panel illustrated in FIG. 1 as a type that detects a magnitude of micro current requires an expensive detection device, there is a problem in that price increases and the multi-touch of recognizing a plurality of touches is difficult.
In order to solve the problem, a capacitive touch screen panel illustrated in FIG. 2 has been primarily used in recent years. The touch screen panel of FIG. 2 is constituted by a horizontal linear touch detection sensor 5a and a vertical linear touch detection sensor 5b, and a touch drive IC 7 analyzing a touch signal. Since the touch screen panel as a type that detects a magnitude of capacitance formed between the linear touch detection sensor 5 and the finger 8 detects a signal by scanning the horizontal linear touch detection sensor 5a and the vertical linear touch detection sensor 5b, a plurality of touch points may be recognized in the touch screen panel.
However, when such a touch screen panel is used while being mounted on a display device such as an LCD, a phenomenon occurs in which it is difficult to detect the signal by noise. For example, the LCD uses a common electrode and in some cases, alternative common voltage Vcom is applied to the common electrode. In addition, the common voltage Vcom of the common electrode serves as the noise when the touch point is detected.
FIG. 3 illustrates an embodiment in which the capacitive touch screen panel in the related art is installed on an LCD. A display device 200 has a structure in which a liquid crystal is enclosed between a TFT substrate 205 at a lower side and a color filter 215 at an upper side to form a liquid crystal layer 210. The TFT substrate 205 and the color filer 215 are bonded to each other by a sealant 230 at outer portions thereof in order to enclose the liquid crystal. Although not illustrated, polarizers are attached to upper and lower sides of a liquid crystal panel and besides, a back light unit (BLU) is installed.
The touch screen panel is installed in an upper portion of the display device 200 as illustrated in FIG. 3. The touch screen panel has a structure in which the linear touch detection sensor 5 is mounted on the top of a substrate 1. A protection panel 3 for protecting the linear touch detection sensor 5 is attached onto the substrate 1. The touch screen panel is bonded to an edge portion of the display device 200 via a bonding member 9 such as a double adhesive tape (DAT), and forms an air gap 9a from the display device 200.
In such a structure, when the touch illustrated in FIG. 3 is generated, capacitance such as Ct is formed between the finger 8 and the linear touch detection sensor 5. However, as illustrated in FIG. 3, capacitance such as common electrode capacitance Cvcom is formed even between the linear touch detection sensor 5 and a common electrode 220 formed on the bottom of the color filter 215 of the display device 200 and Cp which is unknown parasitic capacitance by a capacitance coupling or manufacturing process factor between patterns also acts on the linear touch detection sensor 5. Therefore, a circuit such as an equivalent circuit of FIG. 4 is configured.
Herein, in the touch screen panel in the related art, the touch is recognized by detecting a change amount of Ct which is touch capacitance and components including Cvcom and Cp serve as the noise at the time of detecting Ct. In particular, since the common electrode capacitance Cvcom generated between the pattern and the display device may be ten times or more larger than Ct which is the touch capacitance, there is a problem in that touch sensitivity deteriorates due to Cvcom.